This invention relates to a control apparatus a vehicle for controlling a device mounted thereon.
FIG. 4 shows a typical example of a known control apparatus for a vehicle which includes a temperature sensor 1 mounted on a radiator (not shown) of a vehicle, and a control unit, generally designated by reference numeral 14, for controlling, based on the output of the temperature sensor 1, the operation of a device 16 mounted on the vehicle, the device 16 being in the form of an electric fan motor for air cooling the radiator. The control unit 14 has a first input terminal 2 connected to the temperature sensor 1, a second input terminal 3 connected through a key switch 17 to a DC power source 18 such as a battery, and an output terminal 13 connected to a relay 15 which is connected to the electric fan motor 16 and a node between the second input terminal 3 and the key switch 17. The control unit 14 further includes a main controller 6 in the form of a microcomputer connected to the first input terminal 2 and to the second input terminal 3 through a reset means 5 in the form of a power-on reset element, an abnormality detecting means 7 connected to the microcomputer 6 for detecting an abnormality thereof, an auxiliary controller 9 for controlling the electric fan motor 16 in place of the microcomputer 6 when it is abnormal, a switching means 8 having input terminals connected to the microcomputer 6, the abnormality detecting means 7 and the auxiliary controller 9 and an output terminal connected through a transistor 12 to the output terminal 13 of the control unit 14. The transistor 12 has a base connected through a resistor 11 to the output terminal of the switching means 8, an emitter connected to ground and a collector connected to the output terminal 13. A resistor 4 has one end thereof connected to a 5 volt internal power supply of the control unit 14 and the other end thereof connected to a node between the first input terminal 2 and the microcomputer 6.
With the conventional control apparatus as constructed above, when coolant water in the unillustrated radiator exceeds a prescribed level during the normal operation of the microcomputer 6, the microcomputer 6 senses this situation from the output of the temperature sensor 1 and generates an output which is fed through the resistor 11 to the base of the transistor 12 to turn it on. As a result, the relay 15 is turned on to connect the electric fan motor 16 to the DC power source 18 through the key switch 17 so that the fan motor 16 begins to generate air streams for cooling the radiator. On the other hand, when the microcomputer 6 is abnormal, the abnormality detecting means 7 detects this situation and generates an output to the switching means 8 which is thereby switched over such that the connection between the microcomputer 6 and the transistor 12 is interrupted and instead the auxiliary controller 9 is connected to the transistor 12. As a result, the fan motor 16 is thereafter controlled by the auxiliary controller 9 through the relay 15.
With the above-described conventional control apparatus, however, the abnormality detecting means 7 serves to detect whether the microcomputer 6 is normal or abnormal and, on the other hand, the power-on reset means 5 operates to reset, upon the turning on of the key switch 17, the microcomputer 6 for a predetermined time after which it begins to operate normally. Accordingly, the abnormality detecting means 7 detects an abnormality of the microcomputer 6 at the starting period thereof in addition to the case in which the microcomputer 6 is in fact abnormal. Thus, at the starting time of the microcomputer 6, the switching means 8 is switched over by the abnormality detecting means 7 into a condition in which the auxiliary controller 9 is connected to the relay 15, thereby driving the electric fan motor 16. As a result, when the key switch 17 is turned on by the driver of a vehicle on which the control apparatus is installed, the fan motor 18 is driven to operate for a predetermined period of time which is set by the power-on reset means 5, thus giving rise to an uncomfortable sensation on the part of the driver.